Cannot create correct namespace if the class file name starts with root namespace

[Frederick-S]

Here are the steps to reproduce the issue:

1. Create a console project called Cat, dotnet new console -o Cat
2. Create a folder called Food under Cat
3. Right click the Food folder in VS Code and click new C# Class with the class name CatFood1
4. The namespace of CatFood1 is . instead of Cat.Food

OS: macOS 10.12.5 VS Code: 1.15.0 C# Extensions: 1.3.0